For example, rotating machines such as an electric motor, a generator, a compressor, and a pump include a rotary member rotatable about a predetermined axis. Such rotating machines are used in various plants, and regularly inspected to check the operating state. A tool called a listening rod is used in the inspection. The listening rod is usually made of metal and in the form of a thin rod. In the inspection, a distal end of the listening rod is put on a portion of the rotating machine to be measured and a base end of the listening rod is put on an inspector's ear. Thereafter, the inspector listens to a vibration noise of the rotating machine via the listening rod and determines the presence/absence of an abnormal noise (see Patent Literature 1, for example).
On the other hand, Patent Literature 2, for example, discloses a rotating machine abnormality diagnosis device as a device for making a diagnosis of abnormality in a rotating machine. The rotating machine abnormality diagnosis device disclosed in Patent Literature 2 detects a vibration of the rotating machine and performs a continuous wavelet transform and adds transform signals along the frequency axis to determine whether there is an abnormality or not based on an addition result. In this manner, the rotating machine abnormality diagnosis device disclosed in Patent Literature 2 detects an abnormality due to damage occurring in a bearing of the rotating machine.
By the way, in the abnormality determination of the rotating machine using the listening rod, the accuracy of the determination depends on the expertise of the inspector, and therefore it is difficult to determine the presence/absence of an abnormality objectively and reliably. In particular, an abnormality in the rotating machine is preferred to be detected in its initial stage, but a higher expertise is required for detection of a more initial abnormality.
On the other hand, although the rotating machine abnormality diagnosis device disclosed in Patent Literature 2 determines the presence/absence of an abnormality based on a vibration of the rotating machine, the frequency band that can be recognized as a vibration is a band where a steady vibration such as a so-called characteristic vibration of the device overlaps. This makes it difficult to detect an initial abnormality.